This invention relates to using dioxetanes to detect a substance in a sample.
Dioxetanes are compounds having a 4-membered ring in which 2 of the members are oxygen atoms bonded to each other. Dioxetanes can be thermally or photochemically decomposed to form carbonyl products, i.e., ketones or aldehydes. Release of energy in the form of light (i.e., luminescence) accompanies the decompositions.
In general, the invention features in a first aspect an improvement in an assay method in which a member of a specific binding pair (i.e., two substances which bind specifically to each other) is detected by means of an optically detectable reaction. The improvement includes the reaction, with an enzyme, of
a dioxetane having the formula 
xe2x80x83where T is a substituted (i.e., containing one or more C1-C7 alkyl groups or heteroatom groups, e.g., carbonyl groups) or unsubstituted cycloalkyl (having between 6 and 12 carbon atoms, inclusive, in the ring) or a polycycloalkyl (having 2 or more fused rings, each ring independently having between 5 and 12 carbon atoms, inclusive) group bonded to the 4-membered ring portion of the dioxetane by a spiro linkage; Y is a fluorescent chromophore, (i.e., Y is capable of absorbing energy to form an excited, i.e., higher energy, state, from which it emits light to return to its original energy state); X is H, a straight or branched chain alkyl group (having between 1 and 7 carbon atoms, inclusive, e.g., methyl), straight chain or branched heteroalkyl (having between 1 and 7 carbon atoms, inclusive e.g., methoxy, hydroxyethyl, or hydroxypropyl), aryl (having at least 1 ring, e.g., phenyl), heteroaryl (having at least 1 ring, e.g., pyrrolyl or pyrazolyl), cycloalkyl (having between 3 and 7 carbon atoms, inclusive, in the ring, e.g., cyclohexyl), cycloheteroalkyl (having between 2 and 7 carbon atoms, inclusive, in the ring, e.g., dioxane), aralkyl (having at least 1 ring, e.g., benzyl), or alkaryl (having at least 1 ring, e.g., tolyl), or an enzyme-cleavable group, i.e., a group having a bond which can be cleaved by an enzyme to yield an electron-rich moiety bonded to the dioxetane, e.g., phosphate, where a phosphorus-oxygen bond can be cleaved by an enzyme, e.g., acid phosphatase or alkaline phosphatase to yield a negatively charged oxygen bonded to the dioxetane; and Z is H, OH, or an enzyme-cleavable group (as defined above), provided that at least one of X or Z must be an enzyme-cleavable group,
so that the enzyme cleaves the enzyme-cleavable group to form a negatively charged substituent (e.g., an oxygen anion) bonded to the dioxetane, the negatively charged substituent causing the dioxetane to decompose to form a luminescent substance (i.e., a substance that emits energy in the form of light) that includes group Y. The luminescent substance is detected as an indication of the presence of the first substance. By measuring the intensity of luminescence, the concentration of the first substance can be determined.
In preferred embodiments, one or more of groups T, X, or Y further include a solubilizing substituent, e.g., carboxylic acid, sulfonic acid, or quaternary amino salt; group T of the dioxetane is a polycycloalkyl group, preferably adamantyl; the enzyme-cleavable group includes phosphate; and the enzyme includes phosphatase.
The invention also features a kit for detecting a first substance in a sample.
In a second aspect, the invention features a method of detecting an enzyme in a sample. The method involves contacting the sample with the above-described dioxetane in which group Z is capable of being cleaved by the enzyme being detected. The enzyme cleaves group Z to form a negatively charged substituent (e.g., an oxygen anion) bonded to the dioxetane. This substituent destabilizes the dioxetane, thereby causing the dioxetane to decompose to form a luminescent substance that includes group Y of the dioxetane. The luminescent substance is detected as an indication of the presence of the enzyme. By measuring the intensity of luminescence, the concentration of the enzyme can also be determined.
The invention provides a simple, very sensitive method for detecting substances in samples, e.g., biological samples, and is particularly useful for substances present in low concentrations. Because dioxetane decomposition serves as the excitation energy source for chromophore Y, an external excitation energy source, e.g., light, is not necessary. In addition, because the dioxetane molecules are already in the proper oxidation state for decomposition, it is not necessary to add external oxidants, e.g., H2O2 or O2. Enzyme-triggered decomposition allows for high sensitivity because one enzyme molecule can cause many dioxetane molecules to luminesce, thus creating an amplification effect. Moreover, the wavelength (or energy) of emission and the quantum yields of luminescence can be varied according to the choice of the Y substituent of the dioxetane (as used herein, xe2x80x9cquantum yieldxe2x80x9d refers to the number of photons emitted from the luminescent product per number of moles of dioxetane decomposed). In addition, through appropriate modifications of the T, X, and Y groups of the dioxetane, the solubility of the dioxetane and the kinetics of dioxetane decomposition can be varied. The dioxetanes can also be attached to a variety of molecules, e.g., proteins or haptens, or immobilization substrates, e.g., polymer membranes, or included as a side group in a homopolymer or copolymer.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.